Search results
State which carbocation in each pair below is more stable, or if they are expected to be approximately equal. Explain your reasoning. Answer. 7.10: Carbocation Structure and Stability. It is a general principle in chemistry that the more a charge is dispersed, the more stable is the species carrying the charge.
- Markovnikov's Rule
distinguish among primary, secondary and tertiary...
- The Hammond Postulate
Carbocations become more stable as the number of alkyl...
- Hyperconjugation
This overlap is not strong enough to completely prevent the...
- Markovnikov's Rule
1. Because there are only six valence electrons on carbon and all six are used in the three σ bonds, the p orbital extending above and below the plane is unoccupied. Figure 7.9.1 7.9. 1: The structure of a carbocation. The trivalent carbon is sp2 -hybridized and has a vacant p orbital perpendicular to the plane of the carbon and three attached ...
- What Is A carbocation?
- Formation of Carbocations
- Factors That Stabilize Carbocations – Substitution
- Factors That Stabilize Carbocations – Resonance
- The Importance of Carbocation Stability in Reactions
- Factors That Stabilize Carbocations – Adjacent Lone Pairs
- Which Factor Is More Important – Substitution Or Resonance?
- Some Factors That Destabilize Carbocations
- Some Special Cases
- Summary
A positively charged carbon atom bearing three covalent bonds and an empty orbital is called a carbocation (or more officially, a “carbenium” ion, although for our purposes we’re going to use “carbocation” [Note 1]) Other than the charge of +1 on the central carbon, the structure and properties of the vast majority [Note 2] of carbocations closely ...
Carbocations are important intermediates in many reactions.(An intermediate, as opposed to a transition state, is a potentially isolable species in a reaction and occupies a potential energy minimum in a reaction coordinate diagram. Transition states have partial bonds, extremely short lifetimes and cannot be isolated). Lacking a full octet of elec...
The experimentally measured stability [Note 4] of carbocations shows the following trend: Methyl (least stable) < primary < secondary < tertiary (most stable) In other words, carbocation stability increases as C-H bonds are replaced with C-C bonds. Why? Being electron-poor, carbocations are stabilized through donation of electron density from neigh...
A good working principle in organic chemistry is that concentrated charge is generally more unstable (higher-energy) than dilute charge (lower-energy) [Note 5] One place we’ve seen this before is in the concept of polarizability, where a big anion like iodide I(-) is more stable than a small ion like F(-) because the negative charge is spread out o...
Let’s return to the role of carbocations as intermediates in several key organic reactions. The rate-determining step of the reaction below is protonation of the pi bond with H+ to give a carbocation intermediate. Which of the two reactions do you think is faster? If you answered correctly, congratulations! You’ve shown you understand the reason be...
There’s another factor that stabilizes carbocations that we haven’t touched on yet. If a carbocation is formed adjacent to an atom bearing a lone pair (i.e. a Lewis base) then that atom can donate its pair of electrons to the carbocation, forming a new pi-bond in the process. This is known as “pi-donation” (See article – Pi Donation) It might seem ...
So we have two factors that influence carbocation stability: substitution (primary, secondary, tertiary) and resonance. So which is more important? “they’re bothimportant” is my non-answer to this question. The actual way to answer this question is to look at experimental results. One way to measure carbocation stability is to take a related series...
Since electron-donating groups help to stabilize carbocations, it would make sense to expect that electron-withdrawing groups will destabilize carbocations. As we touched on above, electronegative atoms with lone pairs like O, N, and F that are directly attached to a carbocation will actually help to stabilizecarbocations through pi-donation. I wou...
For the sake of completeness we should probably mention one last factor that is more of a second-semester topic but has a very large impact on the stability of certain carbocations. Some molecules have a particularly stable property known as aromaticity. (See article –Rules For Aromaticity) A related phenomenon called antiaromaticity is responsible...
Carbocations are positively charged, six-electron carbon atoms with an empty p-orbital. They are important intermediates in many reactions and are highly reactive towards Lewis bases. Three key factors stabilize carbocations: 1. First, they are stabilized by adjacent alkyl groups, which can donate electron density to the electron-deficient carbon a...
Carbocations are stabilized when they are adjacent to elements with electron pairs like oxygen, nitrogen, or sulfur. This is because these elements share their electron pairs, leading to a stable resonance structure. Another kind of resonance happens when a carbocation is next to a double bond, making it an allylic carbocation.
Thus, trisubstituted carbocations are more stable than disubstituted ones, which are more stable than monosubstituted ones. The data in Figure 7.11 are taken from measurements made in the gas phase, but a similar stability order is found for carbocations in solution. The dissociation enthalpies are much lower in solution because polar solvents ...
5.2 Carbocation Structure and Stability. To understand why Markovnikov’s rule works, we need to learn more about the structure and stability of carbocations and about the general nature of reactions and transition states. The first point to explore involves structure. A great deal of experimental evidence has shown that carbocations are planar.
People also ask
What is the Order of stability for carbocations?
Are trisubstituted carbocations more stable?
Does the stability of carbocations increase with increasing substitution?
How stable is a carbocation?
How are carbocations stabilized?
Is carbocation a more stable than carbocation B?
Stability of carbocation intermediates. We know that the rate-limiting step of an S N 1 reaction is the first step - formation of the this carbocation intermediate. The rate of this step – and therefore, the rate of the overall substitution reaction – depends on the activation energy for the process in which the bond between the carbon and the leaving group breaks and a carbocation forms.
